1. Field of the Invention
The present invention relates to ion concentration measuring apparatus. More specifically, the present invention is directed to a solid state ion responsive electrode and reference electrode.
2. Description of the Prior Art
Conventional concentration measuring electrode structures have usually used a glass measuring electrode, a reference electrode and a thermal compensator. For example, various types of special glasses have been used to measure the pH of aqueous solutions. In making these glass electrodes the pH sensitive glass is usually fused to the end of a less expensive glass tube and is subsequently blown into a small bulb of about two to four mils thick. These "hand-blown" pH glass electrodes are fragile, have very high electrical impedance due to the thickness of the glass and are used for limited temperature ranges mainly because of the internal pressure developed by a liquid electrolyte fill which is subsequently introduced into the interior of the pH measuring electrode to provide an electrically conductive ion source. An example of a typical prior art pH electrode apparatus is shown in U.S. Pat. No. 3,405,048 of D. J. Soltz. These prior art glass electrodes are expensive mainly because of the extensive use of highly skilled manual labor in the construction of the glass envelope and the subsequent filling thereof. A somewhat similar construction is used in the construction of the prior art reference cell which additionally increases the cost of the overall conventional pH measuring system. Despite its disadvantages, the glass electrode has retained its popularity in the field of ion concentration measurement even after attempts to develop a solid state electrode such as that shown in U.S. Pat. No. 3,498,901 of L. T. Metz et al since the response of the glass electrode is faster than other prior art devices with the glass electrode also having the broadest useful pH range. However, in order to provide a low cost and even more useful ion concentration measuring system it is desirable to produce a low impedance, high reliability and relatively unbreakable pH measuring electrode and reference electrode.